With the rediscovery of the inverse relationship between HDL cholesterol levels and coronary disease risk, the demand for HDL cholesterol quantitation has dramatically increased. While many different methods are used, little work has been done to evaluate specificity (accuracy) or comparability. Thus, current precipitation methods for high density lipoprotein (HDL) quantitation including heparin-Mn2 ion, phosphotungstate-Mg2 ion dextran sulfate-Mg2 ion, heparin-Ca 2 ion and polyethylene glycol, are to be evaluated in terms of their specificity, precision and comparability. The specificity of each method will be evaluated by quantitation of specific apoproteins by immunoassay. Furthermore, the effect of sample handling and storage conditions on the precipitation procedures will be assessed and optimized. Then, an accurate and precise method for HDL quantitation that is suitable for the clinical laboratory will be developed. Since the major differences in HDL levels within a population is predominantly due to the HDL2 subclass, better methods for quantitation of HDL subclasses will also be developed through the application of precipitation procedures and gradient gel electrophoresis and quantitative densitometry. HDL subclasses will be isolated by rate-zonal centrifugation and density gradient ultracentrifugation and characterized by lipid and specific apoprotein quantitation and gradient gel electrophoresis. The apoprotein composition of HDL subclasses will be further examined by quantitative precipitation of 125I labelled HDL with polypeptide specific antisera and polyacrylamide gel electrophoresis and isoelectric focusing. Improvements in the methods to measure and characterize HDL and HDL subclasses should allow a more rational approach to the prevention and treatment of coronary heart disease.